It is known that in an image forming apparatus that has a plurality of image carrying members, which superimpose toner images onto an image transferring member or directly onto a recording sheet (such as paper, for example), a positional deviation of toner images occurs because of fluctuations in the rotational speed of respective image carrying members. In some conventional image forming apparatuses, a pattern is formed on the image transferring member, the positional deviation caused by the fluctuation in the rotational speed of the image carrying members is calculated, and the rotational speed of the image carrying members is controlled to compensate for the positional deviation. Such a conventional technology is disclosed in Japanese Patent Application Laid-Open Publication No. H9-146329. However, if the pattern itself has a positional deviation, precision of compensating for the positional deviation declines.